Current advances in research of biological compounds require sensitive techniques for their separation and analysis. Many of these techniques are based on sample isolation from crude mixtures followed by their further processing, analysis and identification. The separation can be achieved by electromigration in an electric field (electrophoresis), by partitioning between mobile and stationary phases (chromatography) or by combination of the two (electrochromatography). The initial separation can be followed by isolation of separated fractions and their further processing by undergoing various chemical or enzymatic reactions. The resulting products are then visualized and identified by UV or fluorescence signals, mass spectra or NMR spectra and other detection methods.
Many current separation techniques exhibit high resolution and small sample consumption, resulting from miniaturization of separation compartments. Electrophoresis and chromatography is often carried out in narrow-bore columns, fused silica capillaries or miniaturized channels fabricated on silicon chips. In order to isolate the separated compounds, various microscale fraction collection techniques were introduced (See Muller, O; Foret, F.; Karger, B. L.; Design of a high precision fraction collector for capillary electrophoresis. Analytical Chemistry (1995) v. 67, p. 2974–80). The most straightforward technique relies on elution of separated zones into individual collection vessels replaced at the channel exit at time intervals calculated from migration velocity. The more advanced collection devices include sheath flow or moving belt interfaces enabling a semi-continuous operation without a need to interrupt the separation when replacing the collection vessels.
The above mentioned fraction collection techniques are applicable to single channel systems. In order to increase throughput of sample processing, many separations are carried out in a parallel fashion using multiple separation channels. Most common multiplexed separation systems consist of arrays of narrow-bore fused silica capillaries or microfabricated arrays of channels on silicon chips. Currently, there are no commercially available multichannel instruments equipped with an option of isolation and/or fraction collection. The main problem that hinders multichannel collection is the timing, since zones usually elute from different channels at different times. Multichannel collector utilizing multiple individually controlled collection tracks has been proposed (See Irie, T., et al. Automated DNA fragment collection by capillary array gel electrophoresis in search of differentially expressed genes. Electrophoresis (2000) v. 21, p. 367–374) but this approach requires a very complex instrumentation. In addition, only cross-linked separation matrices can be used, to resist laminar flow induced in each separation capillary by the collection sheath flow. An alternative design was demonstrated using a “comprehensive collection” in which zones are collected in predefined time intervals regardless of the actual zone starts and ends. (See Minarik, M.; et al., Design of a fraction collector for capillary electrophoresis. Electrophoresis (2002) v. 23, p. 35–42.) This approach is very effective, however, the total number of capillaries is limited (typically 12 to 16) due to the requirement of capillaries forming a single row cone. This limitation disallows its direct application to currently existing multicapillary instruments (e.g. 8-, 16- or 96-capillary), where capillaries are arranged in a 2-dimensional fashion with rows and columns.
It is an object of the invention to provide means of collecting individual samples from multiple separation channels.
It is a further object of the invention to provide a method allowing collection of compounds from independent channels using a collection device with a simple control.
It is a further object to provide method applicable to available multi-channel separation instruments without a need of complex changes in instrumentation design.